Module 24.1: Overview of the Urinary Systemfalkowl/documents/Urinary_001.pdf · PRINCIPLES OF TUBULAR REABSORPTION AND SECRETION gF3psl.–clTcoIN–8. 85 • _____ – substances

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Urinary System Chapter 24

à Module 24.1: Overview of the Urinary System

• Urinary system (organs of excretion) – composed of a pair of kidneys and urinary tract

o ______________ filter blood to remove metabolic waste products; modify resulting fluid for following purposes:

o Fluid and electrolyte homeostasis

o Acid-base and blood pressure homeostasis

§ Urinary tract – composed of a pair of ureters, urinary bladder, and a single urethra

§ Urine exits kidneys through ______________ found on posterior body wall

§ Each ureter empties into urinary bladder on floor of pelvic cavity where urine is stored

§ Urine exits from urinary bladder through __________; allows urine to exit body

• Kidneys are site where urinary system regulates homeostatic processes:

§ Filter blood to remove metabolic wastes

§ Regulate fluid and electrolyte balance

§

§ Influence blood pressure

§ Releasing hormone erythropoietin (EPO)

OVERVIEWOFTHEURINARYSYSTEMSTRUCTURES

OVERVIEWOFKIDNEYFUNCTION

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Chapters 24 - 25: Urinary System

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§

§

§ Kidneys look like beans in both shape and color

§ Both kidneys are found outside and posterior to peritoneal membrane

(____________________)

§ Right kidney is found in a slightly inferior position due to liver

§ Left kidney is positioned between T12–L3 using vertebral column as reference

§ 11th and 12th ribs provide some protection for both kidneys

§ _____________________ – component of endocrine system; found on superior pole of each kidney

à Module 24.2: Anatomy of the Kidneys

• Three external layers of CT from deep to superficial:

1. __________________ – thin layer of dense irregular connective tissue; covers exterior of each kidney

2. ___________________ – protects from physical trauma

3. ___________________ – dense irregular CT; anchors each kidney to peritoneum and musculature of posterior abdominal wall

• Hilum – opening on medial surface of kidney where renal artery, vein, nerves, and ureters enter and exit

EXTERNALANATOMYOFTHEKIDNEYS

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• Renal cortex and the renal medulla make up urine-forming portion of kidney

§ ________________ 90–95% of all kidney’s blood vessels are found in renal cortex

§ Renal columns – extensions of renal cortex; pass through renal medulla toward renal cortex

• Over one million nephrons are found within cortex and medulla of each kidney

§ Renal corpuscle found in renal cortex

§ Renal tubule found mostly in cortex with some tubules dipping into medulla

• Cone-shaped _______________ are found within renal medulla separated by renal columns on either side

• Each renal pyramid tapers into a slender papilla

à

à

à

à

• Smooth muscle tissue contraction within walls of the calyces and renal pelvis propel urine towards ureter

• Left and right renal arteries are branches of abdominal aorta

1- renal artery à

2- segmental artery à

3- interlobar artery à

INTERNALANATOMYOFTHEKIDNEYS

BLOODSUPPLYOFTHEKIDNEYS

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4- _______________ à

5- interlobular (cortical radiate artery)

• Kidney contains unusual capillary bed system where arterioles both feed and drain capillaries; normally function of a venule

6- afferent arteriole à

7- _________________à

8- efferent arteriole à

9- ________________ capillaries

• Venous blood exits kidney parallel to arterial pathway

10- interlobular veins à

11- arcuate veins à

12- interlobar vein à

13- ________________

§ Renal vein exits kidney from hilum to drain into inferior vena cava

• Nephron – renal corpuscle and renal tubule

§ Renal corpuscle –filters blood

§ 1. __________________ – group of looping fenestrated capillaries

§ 2. Glomerular capsule (Bowman’s capsule) – consists of outer parietal & inner visceral layer

o ____________ space – hollow region between parietal and visceral layers

NEPHRONANDTHECOLLECTINGSYSTEM

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• Filtrate from Bowman’s capsule enters renal tubule:

___________________ (pct)

-

_________________ (descending limb, ascending limb)

-

_________________ (dct)

-

• Juxtaglomerular apparatus (JGA)

- composed of both macula densa and juxtaglomerular (JG) cells;

§ Macula densa is a group of cells in contact with modified smooth muscle cells (juxtaglomerular (JG) cells)

§ JGA regulates blood pressure (BP) and glomerular filtration rate (GFR)

o _______________________________

o ______________________________

§ Collecting system – both medullary collecting duct (cd) and papillary duct that further modify filtrate before it exits kidney

§ cortical cd à medullary cd à ___________________

• Once filtrate enters papillary duct it is known as urine, not filtrate

• Urine exits papillary duct at papilla of renal pyramid into a _________________

• ________________ nephrons make up about 80% of nephrons in kidneys

TYPESOFNEPHRONS

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§ Renal corpuscles are found in outer renal cortex; have short nephron loops that barely enter renal medulla

• ________________ nephrons – much less common than cortical nephrons

§ Renal corpuscles are found near boundary between renal cortex and medulla; have long nephron loops that travel deep within renal medulla

• Cortical nephrons make up about 80% of nephrons in kidneys

§ Renal corpuscles are found in outer renal cortex; have short nephron loops that barely enter renal medulla

• Juxtamedullary nephrons – much less common than cortical nephrons

§ Renal corpuscles are found near boundary between renal cortex and medulla; have long nephron loops that travel deep within renal medulla

Nephrolithiasis

• Formation of renal calculi (_________________); crystalline structures composed most commonly of calcium oxalate salts

• Form when concentrations of ions (also sodium ions, hydrogen ions, and uric acid) are present in filtrate in higher than normal amounts; known as supersaturation

à Module 24.3: Overview of Renal Physiology

• Selectively based on size so _________ and _________________ are not filtered and remain in the circulating blood

GLOMERULARFILTRATION

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§ Smaller substances exit blood to enter capsular space as filtrate

Filtration =

]

• Reclaiming or reabsorbing substances such as water, glucose, amino acids, and electrolytes from tubular fluid to return them into circulating blood

Reabsorption =

• Substances are added into filtrate from peritubular capillaries

§ Helps maintain electrolyte and acid-base homeostasis; removes toxins from blood that did not enter tubular fluid by filtration

Secretion =

à Module 24.4: Renal Physiology I: Glomerular Filtration

• Fenestrated glomerular capillary

§ Fenestrations are large pores

§ Water and small dissolved solutes pass through filtration membrane easily

§ Nitrogenous wastes – group of small substances that are readily filtered; include:

o _________ and ammonium ions (NH4+) from protein metabolism

o Creatinine

o ____________ – product of nucleic acid metabolism

TUBULARREABSORPTION

TUBULARSECRETION

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Filtration Membrane:

1. Fenestrated glomerular __________________ cells 2. Basal lamina 3. Podocytes

Amount of filtrate formed by both kidneys in one minute is known as glomerular filtration rate (GFR); 125 ml/min (________________)

• Net filtration pressure at glomerulus is determined by three driving forces:

1. Glomerular hydrostatic pressure ( ) – blood pressure; higher than average capillary bed hydrostatic pressure

2. Glomerular colloid osmotic pressure ( ) – created mostly by albumin; pulls water back into glomerular capillaries

3. Capsular hydrostatic pressure ( ) – generated as capsular space rapidly fills with new filtrate (10 mm Hg) as fluid can only move so quickly into renal tubule which opposes filtration

• Net filtration pressure (NFP) is combination of these three forces:

NFP = GHP – (GCOP + CHP)

• NFP favors filtration as GHP is greater than sum of forces that oppose filtration (GCOP + CHP)

Glomerulonephritis

• Common condition that involves damage to and destruction of glomeruli; inflammation of glomerular capillaries and basement membrane results

GLOMERULARFILTRATIONRATE

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• Inflammation increases blood flow and capillary permeability; increases GHP; causes filtration membrane to become excessively leaky; leads to loss of blood cells and proteins to urine

Autoregulation – internal kidney mechanisms that work to maintain GFR

• _______________ mechanism – constriction of smooth muscle in blood vessel walls in response to increases in BP

• Tubuloglomerular feedback – uses macula densa of distal renal tubule to control pressure in glomerulus in response to NaCl concentration of filtrate

• Hormonal effects on GFR are part of a larger system that involves regulation of systemic BP and includes angiotensin-II and natriuretic peptides

• Renin-angiotensin-aldosterone system (RAAS) – complex system that maintains systemic BP

• Atrial natriuretic peptide (ANP) – hormone released by heart cells in atria in response to increasing fluid volume; lowers blood volume and BP to reduce workload of the heart

• ANP increases GFR by dilating afferent arterioles and constricting efferent arterioles; increases glomerular hydrostatic pressure

• Neural regulation of GFR primarily involves _______________________ of ANS

• If GFR _____________, kidneys may be unable to carry out their vital functions; called renal failure

§ Renal failure may be a short-term condition known as acute renal failure or acute kidney injury; resolves with treatment

FACTORSTHATAFFECTTHEGLOMERULARFILTRATIONRATE

RENALFAILURE

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§ Renal failure may become chronic after three or more months of decreased GFR; commonly seen with long-standing diabetes mellitus and hypertension

• _________________ – condition that can develop when GFR is less than 50% of normal; leads to buildup of waste products, fluid, electrolytes, as well as acid-base imbalances, all of which can lead to coma, seizures, and death if untreated

• ______________ can be used to treat the signs and symptoms of uremia

The RAAS and Hypertension

• Three classes of drugs have been developed that act on RAAS to reduce blood pressure:

§ ACE inhibitors – developed from snake venom; block ACE; therefore inhibit conversion of angiotensin I to II

§ Angiotensin-receptor blockers – block receptors on blood vessels and proximal tubule cells; prevents vasoconstriction and reabsorption of water and sodium

§ Aldosterone antagonists – block effects of aldosterone on distal tubule; decrease reabsorption of sodium and water; leads to diuretic effect

• Drugs may decrease GFR in patients with pre-existing renal disease; must be monitored

•

à Module 24.5: Renal Physiology II: Tubular Reabsorption and Secretion

• In ___________________, substances pass from filtrate into interstitial fluid then into peritubular capillaries to re-enter blood

• In tubular secretion, substances move in opposite direction

PRINCIPLESOFTUBULARREABSORPTIONANDSECRETION

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• __________________ – substances move from blood into interstitial fluid then into tubule with filtrate

§ Secretion is an active process

• Reabsorption is the main function of ________

§ Large quantity of ions, sodium, potassium, chloride, sulfate, and phosphate; vital to electrolyte homeostasis

§ Almost 100% of nutrients including glucose, amino acids, water-soluble vitamins, and lactic acid

Glycosuria

• Transport maximum – especially important with substances such as glucose • If too much glucose is present in filtrate, TM will be reached before all glucose is reabsorbed; excess will appear in urine (glycosuria)

• Commonly seen in diabetes mellitus – due to defects in production of or response

to insulin; causes inability of cells to take up glucose; leads to high circulating blood glucose (hyperglycemia), high filtrate glucose content, and therefore glucose remaining in urineSecretion in Proximal tubule • Ammonium ions (NH4

+), creatinine, and small amounts of urea are also secreted

• Drugs such as penicillin and morphine have significant renal secretion; must be taken often (typically 3–5 times per day), because amount lost through renal secretion must be replaced in order to maintain relatively consistent blood levels

• Once filtrate reaches nephron loop, 60–70% of water and electrolytes and most organic solutes have been reabsorbed (returned to blood)

REABSORPTIONANDSECRETIONINTHEPROXIMALTUBULE

REABSORPTIONINTHENEPHRONLOOP

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• About 20% of water and 25% of sodium and chloride ions are reabsorbed from loop

Facultative water reabsorption – water is reabsorbed based on body’s needs

• ___________________ –from adrenal cortex; increases reabsorption of

sodium ions from filtrate and secretion of potassium ions into filtrate

• ____________________ (ADH) – from hypothalamus and secreted by posterior pituitary; causes water reabsorption; reduces urine output

• Atrial natriuretic peptide (ANP) – stimulates urinary excretion of sodium ions while it also inhibits release of both aldosterone and ADH

Medullary collecting system – last chance for regulation of fluid, electrolyte, and acid-base balance before filtrate becomes urine

• Impermeable to water in absence of _____________

• Permeable to urea; allows urea to be reabsorbed passively into interstitial fluid

• Cells of proximal tubule secrete hydrogen ions to maintain blood pH

à Module 24.6: Renal Physiology III: Regulation of Urine Concentration and Volume • Kidneys produce dilute urine when solute concentration of extracellular fluid is

too low § § Distal tubule and collecting duct become impermeable to water §

REABSORPTIONANDSECRETION–DISTALTUBULE&COLLECTINGSYSTEM

PRODUCTIONOFDILUTEURINE

COUNTERCURRENTMECHANISM&PRODUCTIONOFCONCENTRATEDURINE

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• Kidneys effectively conserve water by producing very concentrated urine

(reaching nearly 1200 mOsm) using two mechanisms:

§

§ Countercurrent mechanism creates and maintains osmotic gradient by exchanging materials in opposite directions between filtrate and interstitial fluids

§ Countercurrent multiplier proceeds in following steps

§ NaCl is actively transported ___________________ filtrate into interstitial fluid

§ Hypertonic fluid then pulls water out of filtrate in ________________ into interstitial fluid

à Module 24.8: Urine and Renal Clearance

• Urine normally contains:

§

§

§ Potassium

§ Chloride

§

§ Phosphates

§ Sulfates

§ Metabolic wastes such as urea, creatinine, ammonia, and uric acid

§ Small amounts of bicarbonate, calcium, and magnesium may be present

URINECOMPOSITION&URINALYSIS

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§ Urine color

o _______________; breakdown product of hemoglobin

o Darker urine is more concentrated; has less water

o Lighter urine is less concentrated; has more water

§ Urine should be ________________

§ Mild odor; strong odor may be caused by diseases, infections, or by ingesting certain foods

§ Normal pH (6.0); ranges from _______________

§ Specific gravity 1.001 (very dilute) to 1.035 (very concentrated)

§ Renal clearance:

§ Measurement of rate at which kidneys remove a substance from blood

§ For a substance to provide an accurate measure of renal clearance and GFR, substance should be completely filtered and neither reabsorbed nor secreted

§ Creatinine –not totally accurate (5–50% in urine arrived via secretion, not filtration)

§ More accurate assessment of GFR can be obtained using inulin; neither secreted or absorbed; must be injected

à Module 24.9: Urine Transport, Storage, and Elimination

Urinary tract consists of two ureters, urinary bladder, and urethra

• Ureter is 25–30 cm long and empties into bladder

ANATOMYOFTHEURINARYTRACT

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1. ________________ – most superficial layer; made of fibrous connective tissue

2. ________________ – middle layer; made of smooth muscle cells that contract rhythmically (peristalsis) to propel urine toward urinary bladder

3. _______________– deepest layer; mucous membrane composed of transitional epithelium

• Urinary bladder – hollow, distensible organ found on pelvic cavity floor

• _______________ – triangular region on bladder floor; openings of two ureters are found at each posterior corner

• Bladder wall:

1. Adventitia – most superficial layer; made of areolar connective tissue

2. Detrusor muscle – middle layer; squeeze bladder; (internal urethral sphincter) is found at opening of urethra

3. _______________ – innermost layer; made of transitional epithelium

• ________________– drains urine from urinary bladder to outside of body; walls are similar to ureters

• A second external urethral sphincter is formed by levator ani muscle – skeletal muscle of pelvic floor; allows for voluntary control of urination

• Male and female urethra differ structurally and functionally

• Female – about four cm in length; opens at external urethral orifice between vagina and clitoris

• Male – about 20 cm, consists of following three regions:

1. _____________ urethra

2. _____________ urethra

3. _____________ (penile) urethra

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• Micturition – ______________; discharge of urine from urinary bladder to outside of body

• Micturition reflex – reflex arc mediated by parasympathetic nervous system when urine fills bladder and stretches walls:

§ Stretch receptors send a signal to sacral region of the spinal cord via sensory afferent fibers

§ __________________ efferent fibers stimulate detrusor muscle to contract and internal urethral sphincter to relax; allows for micturition

• Micturition center – found in pons (CNS); given time and training makes micturition a voluntary process

MICTURITION

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Fluid, Electrolyte, and Acid-Base Homeostasis

Chapter 25

à Module 25.1: Overview of Fluid, Electrolyte, and Acid-Base Balance

Body fluids – blood plasma, interstitial fluid, cytosol, CSF, lymph and exocrine secretions

- Mostly water

• Fluid balance –maintaining volume and concentration of body’s intracellular (___) and extracellular fluid (___)

• Water that is gained must equal water that is lost

• (H2O in = H2O out)

• Multiple factors impact fluid balance including:

• Amount ingested

•

•

• Medications

• Digestive activities

• Electrolytes – substances that dissociate into ions, or charged particles

§ Electrolytes obtained from diet equals those lost

§ Controlled mostly by ___________________

INTRODUCTIONTOBODYFLUIDS

ELECTROLYTES

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§ Ion concentration is dependent not only on number of ions in a body fluid, but also on amount of water in body fluid

§ Fluid balance is a critical factor that determines electrolyte balance

• An acid is a chemical that dissociates in water to release a _______________ § H+ ion plays a role in: digestion of food, inactivation of microbes and

pathogens, and intracellular digestion in lysosomes • A ___________ or alkali, is a chemical that accepts a H+ or releases a

hydroxide ion (_________) § Bicarbonate and other bases are components of buffer systems

• pH scale – used to measure [H+] of a solution

§ An increase in hydrogen ion concentration results in a solution with a lower pH

§ Solutions with a lower hydrogen ion concentration have a higher pH pH less than 7 are ____________ pH greater than 7 are ____________ pH of 7 are __________ à Module 25.2: Fluid Homeostasis

• Intracellular fluid (ICF); accounts for about 60% of body’s fluids

• Extracellular fluid (ECF) composed of a variety of body fluids

§ ______________ – about 8% of total body water

§ ______________– about 32% of total body water

• Solute composition of ECF and ICF varies

• ___________, chloride, calcium, and bicarbonate ions are higher in ECF

ACIDS,BASES,andpH

FLUIDCOMPARTMENTS

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• _____________, magnesium, sulfate, and monohydrogen phosphate ions higher in cytosol

• Factors that influence water loss – majority of water lost daily is in urine via kidneys

1. Obligatory water loss – (500 ml) urine produced daily irrespective of fluid intake

§ Required to prevent toxic buildup of molecules and electrolyte imbalances

2. Sensible water loss – usually about 100 ml in feces (noticeable amount of water lost)

3. Insensible water loss – usually 600 ml from skin in form of sweat and evaporation

- 300 ml lost in expired humidified air (an unnoticed amount of daily water loss)

§ Most people lose about ______________ of water daily

Fluctuates with water intake, physical activity, and food intake

Water Gains:

1. Water ingested from foods ( )

2. Metabolic water ( )

3. Drinking liquid ( )

Water intake driven by thirst mechanism:

1. Osmoreceptors in hypothalamus

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2. Decreased plasma volume that results in a BP drop detected

by baroreceptors à

Stimulates juxtaglomerular cells à

renin-angiotensin-aldosterone system à angiotensin-II à

_____________________________

• ADH (antidiuretic hormone) plays most important role in balancing water intake with water loss, or fluid balance

§ Produced in hypothalamus and released from posterior pituitary

§ ___________________ and _________________ reabsorb water

§ Increased ADH leads to more water reabsorption that decreases urine volume

§ Decreased ADH leads to more water elimination that increases urine volume

• ________________ – decreased volume and increased concentration of ECF

§ Common causes include: profuse sweating, diarrhea and/or vomiting, some endocrine conditions, and diuretic overuse

§ Water loss decreases plasma volume and increases solute concentration; increases osmotic pressure

• Overhydration (hypotonic hydration) – when ECF volume increases; decreases its osmotic pressure

HORMONALREGULATIONOFFLUIDBALANCE

IMBALANCESOFFLUIDHOMEOSTASIS

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§ ADH secretion is abnormal or an extreme amount of water is consumed in a brief time period (___________________)

§ Electrolyte imbalances, especially sodium ion decreases (hyponatremia) result from diluted ECF

à Module 25.3: Electrolyte Homeostasis

• Sodium ions are most abundant in ECF • Regulation of sodium ion concentration:

§ Angiotensin-II and aldosterone are two main hormones that increase Na+ retention

§ ANP decreases Na+ and water reabsorption

§ Hypernatremia – elevated Na+ concentration; greater than 145 mEq/l; commonly caused by dehydration

§ Hyponatremia – decreased Na+ concentration; less than 135 mEq/l; commonly caused by overhydration

• Potassium ions are most abundant in ICF

• Regulation of potassium ion concentration: § Insulin, aldosterone, and epinephrine are hormones that

stimulate uptake of K+ by cells (endocrine control)

§ Excess K+ is secreted into urine and excreted from body (_______________)

• Hyperkalemia – high K+ in plasma

SODIUM

POTASSIUM

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§ Potentially fatal; resting membrane potential more positive (cells incapable of functioning)

• Hypokalemia – low K+ in plasma § Commonly caused by diuretics that lead to excess K+ loss in

urine § RMP more negative (less responsive to stimuli)

à Module 25.4: Acid-Base Homeostasis

• Normal H+ level in body fluids equals a pH range of about 7.35–7.45

• pH is maintained by:

§ Respiratory and urinary system using two types of buffer systems

1. Chemical buffer systems

2. Physiological buffer systems

Acid-Base Imbalances

• Acidosis - body fluid pH of less than 7.35,

§ More H+ are added

§ Acidosis causes neurons to become less excitable; leads to signs and symptoms of nervous system depression

• Alkalosis - body fluid pH greater than 7.45

§ more base ions are added

§ Increases excitability of neurons causing them to fire APs inappropriately

HYDROGENIONSANDBUFFERINGSYSTEMS

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Documents

Module 24.1: Overview of the Urinary Systemfalkowl/documents/Urinary_001.pdf · PRINCIPLES OF TUBULAR REABSORPTION AND SECRETION gF3psl.–clTcoIN–8. 85 • _____ – substances